Coated grooving or parting insert

ABSTRACT

The present invention relates to a coated cutting tool insert useful for grooving or severing steel components such as steel or stainless steel tubes and bars. The insert is characterized by WC—Co-based cemented carbide substrate having a highly W-alloyed Co-binder phase and a relatively thin coating including an inner layer of TiC x N y O z  with columnar grains followed by a layer of fine grained κ—Al 2 O 3  and a top layer of TiN.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a reissue of U.S. Pat. No. 6,261,673 B1,which claims the benefit of priority to Swedish Application No.9802488-8 filed Jul. 9, 1998.

FIELD OF THE INVENTION

The present invention relates to a coated cemented carbide body. Thepresent invention further relates to a coated cutting tool insert usefulfor grooving or severing steel components such as steel or stainlesssteel tubes and bars.

BACKGROUND OF THE INVENTION

When steel or stainless steel tubes or bars are severed using anappropriate coated cutting tool or cutting tool insert, the cutting edgeis frictionally heated to a high temperature with the consequence thatthe material being cut becomes welded onto the cutting edge of thecutting tool insert. As a result, the coating can flake and smallcemented carbide chips can be torn out of the cutting tool or cuttingtool insert substrate body.

On the other hand, for grooving of the same materials, a high coatingwear resistance in combination with a stiff substrate material isrequired. Finding a cutting tool material that effectively fulfils boththese requirements is a challenge.

So far it has been very difficult to improve all tool propertiessimultaneously. Commercial cemented carbide grades have therefore beenoptimised with respect to one or few of the wear types and hence tospecific application areas.

Swedish patent application 9602413-8 discloses a coated cutting insertparticularly suited for wet turning or grooving stainless steelcomponents. The inserts are characterised by a cemented carbide bodyconsisting of WC—Co and cubic carbides coated by one layer ofTiC_(x)N_(y)O_(z) with columnar grains, one layer of smooth, finegrained κ—Al₂O₃, and preferably an outer layer of TiN.

Swedish patent application 9504304-8 discloses a coated cutting insertparticularly useful for wet and dry milling of low and medium alloyedsteels. The insert is characterised by a cemented carbide substrateconsisting of Co—WC and cubic carbides, a coating including a layer ofTiC_(x)N_(y)O_(z) with columnar grains, a layer of smooth, fine grainedκ—Al₂O₃ and preferably an outer layer of TiN.

SUMMARY OF THE INVENTION

According to the present invention, a combination of the cementedcarbide substrates, coatings and insert styles has been developed whichgives rise to excellent cutting performance in grooving as well assevering of steel or stainless steel.

According to the principles of the present invention, a cutting toolinsert is provided which comprises:

-   -   a cemented carbide body comprising        -   6-15 weight % Co, 0.2-1.8 weight % cubic carbides of Ti, Ta            and/or Nb, a highly W-alloyed binder phase with a CW-ratio            of 0.78-0.93, and the balance WC; and    -   a coating comprising        -   a first innermost layer of TiC_(x)N_(y)O_(z) wherein            x+y+z=1, the first layer having a thickness of 0.1-1.5 μm            and equiaxed grains with size<0.5 μm,        -   a second layer of TiC_(x)N_(y)O_(z) wherein x+y+z=1, the            second layer having a thickness of 0.4-3.9 μm, preferably            1.5-3.0 μm, with coluanar grains with an average diameter of            0.1-5.0 μm,        -   a third layer of a smooth fine-grained κ—Al₂O₃ layer with a            thickness of 0.5-5.5 μm, and        -   the total thickness of the first innermost TiC_(x)N_(y)O_(z)            and the second TiC_(x)N_(y)O_(z) layer is 0.5-4.0 μm, and            the total thickness of all layers is 2.0-6.0 μm, preferably            3.0-5.0 μm.

Further according to the present invention, a method of making a cuttingtool insert comprising a WC—Co-based cemented carbide body with a highlyW-alloyed binder phase and a CW-ratio of 0.78-0.93, the methodcomprising coating the body by:

-   -   forming a first innermost layer of TiC_(x)N_(y)O_(z) with a        CVD-based technique, wherein x+y+z=1, the first layer having a        thickness of 0.1-1.5 μm and equiaxed grains with a size <0.5 μm,        -   forming a second layer of TiC_(x)N_(y)O_(z) by a            MTCVD-technique, wherein x+y+z=1, the second layer having a            thickness of 0.4-3.9 μm and columnar grains with an average            diameter of 0.1-5.0 μm,        -   forming a third layer of a smooth κ—Al₂O₃ having a thickness            of 0.5-5.5 μm, and        -   forming the layers such that the total thickness of the            first and second layers is 0.5-4.0 μm, and the total            thickness of all layers is 2.0-6.0 μm.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows in 1800× magnification of a cross section of an insertaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A cutting tool insert according to the invention useful for severing orgrooving of steel and stainless steel includes a cemented carbidesubstrate with a highly W-alloyed binder phase and with a well balancedchemical composition and grain size of the WC, a columnarTiC_(x)N_(y)O_(z)-layer which layer thickness should be kept as low aspossible, a κ—Al₂O₃-layer, a TiNayer and optionally followed bysmoothening the cutting edges. For example, the edges may be smoothed bybrushing, e.g.—by a SiC-based brush. Surprisingly, beneficial propertieshave been achieved with a relatively thin coating.

The cobalt binder phase is highly alloyed with W. The content of W inthe binder phase can be expressed as the CW-ratio=M_(s)(wt % Co•0.0161),where M_(s) is the measured saturation magnetisation of the cementedcarbide substrate in kA/m hAm² /kg and wt % Co is the weight percentageof Co in the cemented carbide. The CW-value is a function of the Wcontent in the Co binder phase. A low CW-value corresponds to a highW-content in the binder phase. According to the present inventionimproved cutting performance is achieved if the cemented carbidesubstrate has a CW-ratio of 0.78-0.93.

According to the present invention a parting tool insert is providedwith a cemented carbide substrate with a composition of 6-15 wt % Co,preferably 9-12 wt % Co, and most preferably 10-11 wt % Co. Thecomposition further includes 0.2-1.8 wt % cubic carbides, preferably0.4-1.8 wt % cubic carbides, most preferably 0.5-1.7 wt % cubiccarbides, of the metals Ta, Nb and Ti and balance WC. The cementedcarbide may also contain other carbides from elements from group IVb, Vbor VIb of the periodic table. The content of Ti is preferably on a levelcorresponding to a technical impurity. The preferred average grain sizeof the WC depend on the binder phase content. At a preferred compositionof 10-11 wt-% Co, the preferred grain size is 1.5-2.0 μm, mostpreferably about 1.7 μm. The CW-ratio shall be 0.78-0.93, preferably0.80-0.91, and most preferably 0.82-0.90. The cemented carbide maycontain small amounts, <1 volume %, of ρ-phase (M₆C), without anydetrimental effect. From the CW-value it follows that no free graphiteis allowed in the cemented carbide substrate according to the presentembodiment.

The coating comprises a first innermost layer of TiC_(x)N_(y)O_(z) withx+y+z=1, preferably y>x and z<0.2, most preferably y>0.8 and z=0, withequiaxed grains with a size <0.5 μm, and a total thickness <1.5 μmbut >0.1 μm, preferably the thickness is 0.1-0.6 μm;

-   -   a second layer of TiC_(x)N_(y)O_(z) with x+y+z=1, preferably        with z=0, x>0.3 and y>0.3, most preferably x>0.5, with a        thickness of 0.4-3.9 μm, preferably the thickness is 1.5-3.0 μm,        the second layer has columnar grains with an average diameter of        <5 μm, preferably 0.1-2.0 μm;    -   the total thickness of the first and second layers is 0.5-4.0        μm, preferably 1.5-3.5 μm. Preferably, the first layer is        thinner than the second layer;    -   a third layer of a smooth, fine-grained Al₂O₃ consisting        essentially of the κ-phase having a grain size about 0.5-2 μm.        However, the layer may contain small amounts, 1-3 vol-%, of the        θ or the α-phases as determined by x-ray diffraction (XRD)        measurement. The Al₂O₃-layer has a thickness of 0.5-5.5 μm,        preferably 0.5-3.0 μm;    -   preferably, this Al₂O₃-layer is followed by a further layer of        TiN having a thickness <1 μm, preferably 0.1-0.5 μm thick. The        Al₂O₃ or the TiN layer can be the outermost layer. This        outermost layer, whether Al₂O₃ or TiN, has a surface roughness        R_(max)<0.4 μm over a length of 10 μm. The TiN-layer, if        present, is preferably removed along the cutting edge by a        suitable removal technique, such as brushing; and    -   the total thickness of the first, second and third layers is 2-6        μm, preferably 3-5 μm.

According to a method of the invention, a WC—Co-based cemented carbidesubstrate is made with a highly W-alloyed binder phase with a CW-ratioof 0.78-0.93, preferably 0.80-0.91, and most preferably 0.82-0.90. Thecontent of cubic carbides of the metals Ta, Nb and Ti is 0.2-1.8 wt %,preferably 0.4-1.8 wt %, and most preferably 0.5-1.7 wt %. The substratefurther includes 6-15 wt % Co, preferably 9-12 wt % Co, and mostpreferably 10-11 wt % Co. The WC grain size is 1.5-2.0 μm, mostpreferably about 1.7 μm, when the Co content is in the 10-11 wt. %range. The body is coated by:

-   -   a first innermost layer of TiC_(x)N_(y)O_(z) with x+y+z=1,        preferably y>x and z<0.2, most preferably y>0.8 and z=0, with        equiaxed grains with size <0.5 μm and a total thickness <1.5 μm,        preferably >0.1 μm, preferably 0.1-0.6 μm, using known        CVD-methods;    -   a second layer of TiC_(x)N_(y)O_(z) with x+y+z=1, preferably        with z=0, x>0.3 and y>0.3, most preferably x>0.5, with a        thickness of 0.4-3.9 μm, preferably 1.5-3.0 μm, with columnar        grains and with an average diameter of about <5 μm, preferably        0.1-2.0 μm, is applied preferably using a MTCVD-technique        (e.g.—using acetonitrile as the carbon and nitrogen source for        forming the layer in the temperature range of 700-900° C.). The        exact conditions, however, depend to a certain extent on the        design of the equipment used;    -   the total thickness of the first and second layers is 0.5-4.0        μm, preferably 1.5-3.5 μm. Preferably, the first layer is        thinner than the second layer;    -   a third layer of a smooth, fine-grained Al₂O₃ consisting        essentially of the κ-phase having a grain size about 0.5-2.0 μm.        The Al₂O₃-layer has a thickness of 0.5-5.5 μm, preferably        0.5-3.0 μm. Preferably, this Al₂O₃-layer is followed by a        further layer of TiN having a thickness <1 μm, preferably        0.1-0.5 μm thick. The Al₂O₃ layer can be exposed as the        outermost layer. The outermost layer of Al₂O₃ or TiN has a        surface roughness R_(max)<0.4 μm over a length of 10.0 μm. The        smooth coating surface can be obtained by gently wet-blasting        the coating surface with fine grained (400-150 mesh) alumina        powder, or by brushing (preferably used when TiN top layer is        present) the edges with brushes based on SiC as disclosed in        Swedish patent application 9402543-4. The TiN-layer, if present,        is preferably removed along the cutting edge; and    -   the total thickness of the first, second and third layers is        2.0-6.0 μm, preferably 3.0-5.0 μm.

As a way of further illustrating the present invention and theadvantages thereof, the following examples are given.

EXAMPLE 1

A. A cemented carbide cutting tool insert in style N151.2-300-5E withthe composition 10.5 wt-% Co, 1.16 wt-% Ta, 0.28 wt-% Nb and balance WC,with a binder phase highly alloyed with W corresponding to a CW-ratio of0.87, was coated with an innermost 0.5 μm equiaxedTiC_(0.05)N_(0.95)-layer with a high nitrogen content, corresponding toan estimated C/N ratio of 0.05, followed by a 2.2 μm thick layer ofcolumnar TiCo_(0.54)N_(0.46) deposited using MT-CVD technique. Insubsequent steps during the same coating process a 1.5 μm layer of Al₂O₃consisting of pure ic-phase was formed according to procedure disclosedin EP-A-523 021. A thin, 0.5 μm, TiN layer was deposited, during thesame cycle, on top of the Al₂O₃-layer. Hence, the total thickness of alllayers is 4.7 μm. The coated insert was brushed by a SiC containingnylon straw brush after coating, removing the outer TiN layer on theedge.

B. A cemented carbide cutting tool insert in style N151.2-300-SE withthe composition of 8.0 wt-% Co, no cubic carbides, balance WC and aCW-ratio of 0.94 was prepared. The insert was coated with an innermost0.5 μm equiaxed TiCN-layer. A 1.5 μm TiN layer was deposited, during thesame cycle, on top of the TiCN-layer. No post treatment was applied.

C. A cemented carbide cutting tool insert in style N151.2-300-SE withthe composition of 8.0 wt-% Co, no cubic carbides, balance WC and aCW-ratio of 0.94. The insert was coated with an innermost 0.5 μmequiaxed TiCN-layer with a high nitrogen content, corresponding to anestimated C/N ratio of 0.05, followed by a 4.0 μm thick layer ofcolumnar TiCN deposited using MT-CVD technique. In subsequent stepsduring the same coating process a 1.0 μm layer of Al₂O₃ consisting ofpure K phase was formed according to procedure disclosed inEP-A-523-021. A thin, 0.5 μm TiN layer was deposited, during the samecycle, on top of the Al₂O₃-layer. The coated insert was brushed by a SiCcontaining nylon straw brush after coating, removing the outer TiN layeron the edge.

D. A comparative cemented carbide cutting tool insert in style similarto N151.2-300-5E from an external leading cemented carbide producer wasselected for comparison. The carbide had a composition of 11.0 wt-% Co,7.1 wt-% TiC, 12.1 wt-% TaC, 1.3 wt-% NbC, balance WC and a CW-ratio of0.80. The insert had a coating consisting of 1.1 μm TiN and, outermost,0.3 μm TiCN layer. Examination in light optical microscope revealed noedge treatment subsequent to coating.

Inserts from A, B and C were compared in a flaking test comprising afacing operation in austenitic stainless steel (SanMac 304L). Feed 0.15mm/rev, speed 130 m/min and depth of cut varying between 0-2.5 mm.

Number of cuts before extensive Insert flaking A (acc. to invention) 10 B (outside invention) 5 C (outside invention) 1 D (external grade) 3

EXAMPLE 2

Inserts A, B, C and D from above were tested in a serving test ofstainless steel (SS2343) in the form of 12 mm bar stainless steel.

The rotating speed was 1800 rpm, feed varying 0.15-0.02 mm/rev (low feedrate close to centre of bar).

The wear mechanism was flaking combined with nose cracking.

Insert Number of components A (acc. to invent.) 380 B (outsideinvention) 180 C (outside invention) 200 D (external grade) 200

EXAMPLE 3

Inserts A (insert style N151.2-400-4E) and D were tested at an end usersmachine shop in severing of stainless steel tube (SS2343, OD 27 mm, ID25 mm) with feed 0.05 mm/rev and speed 150 m/min.

Insert D failed due to major chipping of the cutting edge while a verysmall chipping was seen on insert A.

Insert Number of components A (acc. to invention) 324 D (external grade)108

EXAMPLE 4

Inserts A and D were tested at an end users machine shop in parting tocentre of an annealed high alloy steel SS2242 with feed 0.15 mmlrev andspeed 100 m/min.

Insert D failed due to cracking in the corners while a very smalldeformation in the corners was seen on insert A.

Insert Number of components A (acc. to invention) 400 D (external grade)150

EXAMPLE 5

Inserts A (insert style N151.2-400-4E) and D were tested at an end usersmachine shop in parting of a steel bar (SS2225, OD 50 mm) with feed0.06-0.14 mm/rev and speed 180 m/min.

Insert D failed due to chipping of the cutting edge while even flankwear was seen on insert A.

Insert Number of components A (acc. to invention) 300 D (external grade)150

While the present invention has been described by reference to theabove-described embodiments, certain modifications and variations willbe evident to those of ordinary skill in the art. Therefore, the presentinvention is to limited only the scope and spirit of the appendedclaims.

1. A cutting tool insert comprising: a cemented carbide body comprising6-15 weight % Co, 0.2-1.8 weight % cubic carbides of Ti, Ta, Nb or anycombination thereof, a highly W-alloyed binder phase with a CW-ratio of0.78-0.93, and the balance WC; and a coating comprising a firstinnermost layer of TiC_(x)N_(y)O_(z) wherein x+y+z=1, the first layerhaving a thickness of 0.1-1.5 μm and equiaxed grains with size <0.5 μm,a second layer of TiC_(x)N_(y)O_(z) wherein x+y+z=1, the second layerhaving a thickness of 0.4-3.9 μm, with columnar grains with an averagediameter of 0.1-5.0 μm, a third layer of a smooth fine-grained κ—Al₂O₃layer with a thickness of 0.5-5.5 μm, and a total thickness of the firstinnermost TiC_(x)N_(y)O_(z) and the second TiC_(x)N_(y)O_(z) layer is0.5-4.0 μm, and the total thickness of all layers is 2.0-6.0 μm.
 2. Thecutting tool insert of claim 1, wherein the body comprises 9-12 weight %Co and a CW ratio of 0.80-0.91.
 3. The cutting tool inset of claim 1,wherein in the first layer y>x and z<0.2, and the thickness of the firstlayer is 0.1-0.6 μm.
 4. The cutting tool insert of claim 1, wherein inthe second layer z=0, x>0.3 and y>0.3, the second layer has a thicknessof 1.5-3.0 μm, with the columnar grains having an average diameter of0.1-2.0 μm.
 5. The cutting tool insert of claim 1, wherein in the thirdlayer the grains of the κ—Al₂O₃ have a size on the order of 0.5-2.0 μm,and the third layer has a thickness of 0.5-3.0 μm.
 6. The cutting toolinsert of claim 1, wherein the total thickness of the first and secondlayers is 1.5-3.5 μm.
 7. The cutting tool insert of claim 1, wherein thetotal thickness of all the layers is 3.0-5.0 μm.
 8. The cutting insertof claim 1 further comprising an outermost layer of TiN having athickness of 0.1-1.0 μm.
 9. The cutting insert of claim 8, wherein theoutermost TiN-layer has been removed along the cutting edge.
 10. Amethod of making a cutting tool insert comprising a WC—Co-based cementedcarbide body with a highly W-alloyed binder phase and a CW-ratio of0.78-0.93, the method comprising coating the body by the steps of:forming a first innermost layer of TiC_(x)N_(y)O_(z) with a CVD-basedtechnique, wherein x+y+z=1, the first layer having a thickness of0.1-1.5 μm and equiaxed grains with a size <0.5 μm, forming a secondlayer of TiC_(x)N_(y)O_(z) by a MTCVD-technique, wherein x+y+z=1, thesecond layer having a thickness of 0.4-3.9 μm and columnar grains withan average diameter of 0.1-5.0 μm, forming a third layer of a smoothκ-Al₂O₃ having a thickness of 0.5-5.5 μm, and forming the layers suchthat the total thickness of the first and second layers is 0.5-4.0 μm,and the total thickness of all layers is 2.0-6.0 μm.
 11. The method ofclaim 10, wherein the step of forming the first layer further comprisesproviding the first layer with y>x and z<0.2 and a thickness of 0.1-0.6μm.
 12. The method of claim 10 wherein the step of forming the secondlayer further comprises using acetonitrile as the carbon and nitrogensource and forming the second layer at a temperature of 850-900° C., thestep of forming the second layer further comprises providing z=0, x>0.3and y>0.3, a thickness of 1.5-3.0 μm, and with the columnar grainshaving an average diameter of 0.1-2.0 μm.
 13. The method of claim 10,wherein the third layer is provided with a thickness of 0.5-3.0 μm. 14.The method of claim 10, wherein the method further comprises forming anouter layer of TiN having a thickness of <1 μm.
 15. The method of claim10, wherein the method further comprises providing the first and secondlayers with a total thickness of 1.5-3.5 μm, and a total thickness ofall layers of 3.0-5.0 μm.
 16. The method of claim 10 wherein the saidcemented carbide body has a cobalt content of 9-12 weight % and 0.4-1.8weight % cubic carbides of Ta and Nb.
 17. The method of claim 10 whereinthe cemented carbide body has a cobalt content of 10-11 weight %. 18.The method of claim 17 wherein the cemented carbide body has a CW-ratioof 0.82-0.90.
 19. The method of claim 14, wherein the outermostTiN-layer is removed along a cutting edge.
 20. The method of claim 19,wherein the outermost TiN-layer is removed by brushing.
 21. The cuttingtool inset of claim 3, wherein in the second layer z=0, x>0.3 and y>0.3,the second layer has a thickness of 1.5-3.0 μm with the columnar grainshaving an average diameter of 0.1-2.0 μm.
 22. The cutting tool insert ofclaim 21, wherein in the third layer the grains of the κ-Al₂ O ₃ have asize on the order of 0.5-2.0 μm and the third layer has a thickness of0.5-3.0 μm.
 23. The cutting tool insert of claim 22, wherein the totalthickness of all the layers is 3.0-5.0 μm.
 24. The cutting insert ofclaim 22 further comprising an outermost layer of TiN having a thicknessof 0.1-1.0 μm.
 25. The cutting insert of claim 24, wherein the outermostTiN-layer has been removed along the cutting edge.
 26. The method ofclaim 11 wherein the step of forming the second layer further comprisesusing acetonitrile as the carbon and nitrogen source and forming thesecond layer at a temperature of 850-900° C., the step of forming thesecond layer further comprises providing z=0, x>0.3 and y>0.3, athickness of 1.5-3.0 μm and with the columnar grains having an averagediameter of 0.1-2.0 μm.
 27. The method of claim 26, wherein the methodfurther comprises forming an outer layer of TiN having a thickness of <1μm.
 28. The method of claim 27, wherein the outermost TiN-layer isremoved along a cutting edge.
 29. The method of claim 26, wherein themethod further comprises providing the first and second layers with atotal thickness of 1.5-3.5 μm and a total thickness of all layers of3.0-5.0 μm.
 30. The method of claim 10 wherein the said cemented carbidebody has a cobalt content of 9-12 weight % and 0.4-1.8 weight % cubiccarbides of Ta and Nb.
 31. The method of claim 30 wherein the cementedcarbide body has a CW-ratio of 0.82-0.90.